The present invention relates generally to printed circuit boards, and more particularly, to a method for forming components used in the manufacturing of printed circuit boards and other articles.
In the manufacture of printed circuit boards, sheets of copper foil are typically bonded to a dielectric layer of a partially cured epoxy resin containing woven glass fiber (such a dielectric layer is conventionally referred to as a xe2x80x9cprepregxe2x80x9d). In the manufacture of copper clad laminates, sheets of copper foil are typically bonded to another layer of foil. In both processes, the copper foil is etched to produce conductive paths. In recent years, the trend has been to reduce the size of electronic components, and to increase the number of such components provided on a printed circuit board. A key to providing a densely populated circuit board is to produce close and fine circuit patterns from the copper. This in turn has resulted in a drive to provide laminates having thinner and thinner layers of copper thereon.
A problem with copper foils is that at a certain thickness (about 0.5 oz. per square foot), the copper foil becomes very difficult to handle. It has been known to apply copper onto temporary carrier sheets such as plastic and metal for later transfer to dielectric layers or another copper layer. Depositing their copper on these carrier layers adds another step in the manufacturing process preceding the attachment of the copper to a dielectric substrate.
The present invention provides a method of forming components used in the manufacture of printed circuit boards, which components have thin layers of copper thereon.
In accordance with a preferred embodiment of the present invention, there is a method of forming a laminate used in the manufacture of printed circuit boards. The method comprises the steps of:
applying a layer of chromium having a thickness from about 30 grams per square meter to about 160 grams per square meter to each side of a steel substrate having a thickness from about 0.10 mm to about 0.20 mm;
applying a layer of copper having a thickness from about 2 xcexcm to about 70 xcexcm to each of said chromium layers;
positioning said steel substrate between two dielectric layers with adhesive disposed between said copper layers and said dielectric layers;
applying heat and pressure to said layers to bond said copper layers to said dielectric layers;
separating said steel substrate from said copper layers; and
discarding said steel substrate.
It is an object of the present invention to provide a component having a copper layer for use in manufacturing articles such as printed circuit boards.
It is a further object of the present invention to provide a component as described above wherein the metallic substrate is a relatively low-cost, discardable item.
It is a further object of the present invention to provide a component as described above wherein the metallic substrate is formed of carbon steel and has an outer layer of an inert metal thereon for engagement with a copper sheet.
It is a further object of the present invention to provide a component as described above wherein the inert metal is chromium.
It is another object of the present invention to provide a component as described above that is suitable for high-temperature processing applications.
A still further object of the present invention to provide a component as described above wherein the discardable metallic substrate has a co-efficient of thermal expansion approximately equal to the co-efficient of thermal expansion of pressed plates used in forming laminated printed circuits.
A still further object of the present invention is to provide a component as described above wherein the metallic substrate is dimensioned for use as a press plate in a circuit board forming operation.
A still further object of the present invention is to provide a method of forming the above-identified component that is used in manufacturing articles such as printed circuit boards.
These and other objects will become apparent from the following description of a preferred embodiment taken together with the accompanying drawings.